Selective production of olefins and hydrogen from waste plastics via a thermal plasma-assisted pyrolysis system

<title>Abstract</title> <p> Waste polypropylene (WPP) is a major waste and remains difficult to treat through conventional recycling methods because of contamination, property deterioration, and limited product selectivity. A coupled thermal plasma-assisted pyrolysis system was developed to convert WPP into light olefins or hydrogen in this study. WPP was first pyrolyzed in a screw-type pyrolysis reactor at 480 ℃ to generate hydrocarbon vapors, which were then directly introduced into a DC arc plasma. Under pyrolysis-only conditions, the product distribution was dominated by liquid of 82.56 wt.%, whereas the gas was limited to 7.14 wt.%, indicating limited cracking efficiency. In contrast, all products were converted toward gaseous hydrocarbons, particularly C ₂ –C ₄ olefins by a plasma-assisted pyrolysis system converted. Increasing the N ₂ flow rate from 20 to 40 L/min at an arc current of 40 A in plasma increased the olefin fraction from 50.8 to 67.0 wt.% while decreasing acetylene in product gas. The optimal condition was identified at 50 A and 40 L/min N ₂ , achieving the olefin yield of 69.0 wt.%. In particular, reducing the reaction region intensified plasma–gas interactions, ultimately producing hydrogen-rich gas. The invented thermal plasma-assisted pyrolysis system could be a robust tool to produce valuable chemical feedstocks with tunable selectivity from WPP without catalysts. </p>